FISHERY BULLETIN: VOL. 77, NO. 4 



FIGURE 12 — Cumulative record of time 

 of first sighting, onset of rest, waken- 

 ing, etc. 



the point were not kept. Our efforts at listening to 

 dolphins in Kealakekua Bay showed that dolphins 

 at the mouth of the bay can easily hear those in its 

 deepest recesses, so the effect may be one of exclu- 

 sion of the passing school by occupants. The point 

 needs further study. 



Small schools often seemed to coalesce upon ar- 

 rival in the bay. This first became apparent when 

 our estimates of school size during an arrival 

 sequence increased sharply, or even doubled, be- 

 tween the time the animals were at the bay en- 

 trance and when they were deeper in the bay. In 

 other records such obvious increase in school size 

 occurred after the animals were deep in the bay. 

 The arrival of such supplementary schools was 

 occasionally observed and their coalescence into a 

 single school noted. 



School structure during entry was best observed 

 in those that entered in the central sector, without 

 the visual interference of headlands or the swells 

 and breakers that sometimes obscured sightings 

 close to shore. Such schools were sometimes first 

 seen as far as 4 km beyond the bay and could be 

 watched during the entire entry traverse. These 

 schools typically swam in a ragged rank composed 

 of quite discrete groups. The dolphins were often 

 quite active, and their passage was accompanied 



by spins and other aerial behavior. Often, by the 

 time the bay mouth was reached aerial behavior 

 had subsided considerably, though it often per- 

 sisted to some degree for as long as 2 h after initial 

 entry. In small schools of approximately 6-15 ani- 

 mals, entry was often quite unobtrusive. In spite of 

 a conscientious watch from the clifftop during 

 early morning hours such small schools were 

 sometimes seen first deep in the bay. Large schools 

 typically exhibited more aerial activity than small 

 ones, and it appeared to persist for a longer period. 

 Arriving dolphin schools often come to the bows 

 of vessels where they engage in assisted locomo- 

 tion or "bowriding" (Norris and Prescott 1961). 

 Even so, if a vessel pursued such schools, re- 

 peatedly making passes through their ranks or 

 changing speeds upon approach, the school usu- 

 ally edged toward deep water, and if the harass- 

 ment continued, the school left the bay. Observers 

 on shipboard usually failed to note the effect on the 

 school as a whole, since their attention was fo- 

 cused on the bowriding animals. But an observer 

 on the cliff above the bay, watching the entire 

 school, could quickly discern this retreat. This ef- 

 fect nearly always occurred, even if the intruding 

 vessel moved very carefully. Later, when the 

 school had subsided into quiescence, it was much 



838 



